JP3005289B2 - Ozonation of hydrogenated latex - Google Patents

Description

BACKGROUND OF THE INVENTION In some cases, it is desirable to hydrogenate rubber to improve its resistance to oxidation and thermal degradation. For example, it is sometimes beneficial to hydrogenate nitrile rubbers used in applications exposed to high operating temperatures.
Hydrogenation of polymers is generally carried out by solution methods that require the use of highly reactive chemicals or heterogeneous catalysts. Unfortunately, these methods pose handling and use difficulties. However, these difficulties are overcome by hydrogenating the rubber in latex form as described in Lawson G. Weideman, U.S. Pat. No. 4,452,950.

The method described by Weideman involves hydrogenating the carbon-carbon double bond of an unsaturated polymer, wherein (a) converting the latex-like unsaturated polymer from (1) the group consisting of oxygen, air and hydroperoxides. An oxidant of choice; (2) a reducing agent selected from the group consisting of hydrazine and its hydrates; and (3) mixed with a metal ion initiator; and (b) a temperature of the mixture from 0 ° C. to the reflux temperature of the reaction mixture. Heating. Hydrogenation of latex-like elastic polymers by the Weideman method has of course many advantages. However, to make the method described by Weideman commercially viable,
There are difficulties to overcome. When a high degree of unsaturation is achieved, for example by the Weideman method, crosslinking of the polymer generally occurs within the individual latex particles. This is due to the crosslinking of the elastic polymer that occurs during the reduction operation. Usually, it is preferred that the elastic polymer is not cross-linked, so this cross-linking is often undesirable. Another problem encountered is the presence of residual hydrazine in the emulsion of the hydrogenated elastomeric polymer. The presence of high levels of residual hydrazine in the latex is not commercially acceptable. In fact, levels of residual hydrazine in the latex above about 10 ppm are highly undesirable. In most cases, it is preferred that the concentration of residual hydrazine in the latex be less than about 4 ppm.

SUMMARY OF THE INVENTION The practice of the present invention allows the treatment of an elastic polymer that has been reduced in latex form by the Weideman method to remove gels and at the same time reduce the concentration of residual hydrazine present in the latex. This method treats the reduced latex with ozone, which performs a dual function of reducing the level of gelled (cross-linked) polymer and residual hydrazine in the latex. This is a colored body that may be present in the reduced latex,
For example, removing benzoquinone also improves latex color.

In particular, the present invention relates to a method of treating an emulsion of a crosslinked elastic polymer containing residual hydrazine to obtain a latex of a soluble (non-crosslinked) elastic polymer having a reduced residual hydrazine concentration. Disclosed is a method comprising adding sufficient amount of ozone thereto under sufficient conditions to react with hydrazine to form a latex of a soluble (non-crosslinked) elastomeric polymer having reduced residual hydrazine levels.

The invention comprises a method of reducing the residual hydrazine concentration of an emulsion of an elastomeric polymer, comprising treating the emulsion with a sufficient amount of ozone to reduce the residual hydrazine concentration of the emulsion under conditions sufficient thereto. A method is also disclosed.

DETAILED DESCRIPTION OF THE INVENTION Emulsions treated according to the present invention are usually prepared by the method of Weideman (U.S. Pat. No. 4,452,950). The entire teachings of this specification are incorporated herein by reference. Weidemann's teaching essentially hydrogenates the carbon-carbon double bonds of a latex-like unsaturated elastomeric polymer and converts the unsaturated elastomeric polymer latex from the group consisting of (1) oxygen, air and hydroperoxides. (2) a reducing agent selected from the group consisting of hydrazine and hydrazine hydrate; and (3) a metal ion-based activator. The hydrogenation reaction may be performed at a temperature substantially anywhere from about 0 to about 300 ° C. In general, it is preferred to carry out the hydrogenation reaction at a temperature of about 20 to about 150 ° C., and to ensure selective hydrogenation and to suppress undesirable side reactions, 100 ° C.
The following temperatures are highly preferred: This hydrogenation reaction is generally carried out at a temperature from atmospheric pressure to 300 kg / cm ² .

In carrying out the Weideman hydrogenation method, oxygen is generally used. However, air or other oxidants such as hydrogen peroxide, cumyl hydroperoxide, t-butyl hydroperoxide, p-methane hydroperoxide and the like can also be used. A wide variety of metals or salts, including ions that react with hydrazine, can be used as metal ion based activators. Antimony, arsenic, bismuth, cerium, chromium, cobalt, copper, gold, iron,
Lead, manganese, mercury, molybdenum, nickel, osmium, palladium, platinum, cerium, silver, tellurium, tin and vanadium react with hydrazine and therefore contain ions that are useful as metal ion activators in Weidemann's hydrogenation process Representative examples of metals or salts. Iron and copper are the preferred metal ion based activators, with iron being highly preferred.

Various substances such as hydroquinone, catechol,
It is also well known that quinone, o-phenylenediamine and cerium catalyze the reaction of hydrazine with hydrogen peroxide or oxygen. This type of reaction is described in Zong and Rim (Zhon
g, Lim), “Copper-catalyzed redox reaction of aqueous hydrogen peroxide with hydrazine. 1. New experimental results and findings”, Journal
of The American Chemical Society, Vol. 111, No.
22, p. 8398-8404 (1989), page 8401.
According to the teachings of Tsong and Rim, hydroquinone can be used to catalyze the reaction of oxygen with residual hydrazine in an aqueous emulsion of rubber prepared by the method of Weideman. By employing this method, the level of residual hydrazine in the latex can be reduced to a general level of about 1-2.
% To about 50 to about 100 ppm. This can be achieved by simply mixing oxygen and a small amount of a catalyst such as hydroquinone, catechol, quinone or o-phenylenediamine into the residual hydrazine-containing latex. This method is facilitated by increasing the catalyst concentration, temperature and oxygen pressure as desired. Generally about 0.001 to about 1 phr (parts by weight per 100 parts rubber) of the catalyst is used. In most cases, the amount of catalyst used is about 0.05
-About 0.25 phr. Unfortunately, this method is not a complete solution to the problem, as it does not usually reduce the level of residual hydrazine to very low levels, which is aimed at. However, it is often desirable to utilize this unfinished method as an intermediate means to reduce the level of residual hydrazine in the latex. That is, the latex is first treated with oxygen or hydrogen peroxide to reduce the level of residual hydrazine in the latex to about 50-100 ppm,
It is often desirable to treat the latex with ozone in accordance with the present invention.

Virtually any type of hydrogenated rubber latex can be treated by the method of the present invention. For example, the latex is polybutadiene rubber, polyisoprene, nitrile rubber, carboxylated nitrile rubber, styrene-butadiene rubber, styrene-isoprene-butadiene rubber, or the like. These hydrogenated rubbers generally have a saturation level of about 90 to about 99%. Preferably, the hydrogenated rubber has a saturation level of about 95% to about 98%. In practicing the present invention, the latex is simply mixed with ozone for a period sufficient to achieve the desired result. This can be achieved by blowing ozone into the latex. This can also be accomplished by stirring the latex in an atmosphere containing ozone. The atmosphere containing ozone is desirably under pressure. Other methods of mixing ozone throughout the latex to be treated may be employed in the practice of the present invention. The temperature at which this process is performed is not critical. In fact, virtually any temperature between the freezing temperature of the latex and its boiling point can be employed. However, for practical purposes, the latex is usually treated with ozone at a temperature of about 0 to about 60 ° C. It is highly preferred to use a temperature of about 15 to about 30 ° C.
Higher temperatures achieve higher reaction rates, but may reduce the solubility of ozone in the latex. The ozonation is performed for a time sufficient to remove undesirable levels of cross-linking and sufficient to reduce the hydrazine concentration to acceptable levels. The treatment period employed is generally from about 15 minutes to about 6 hours. The period used to treat the latex with ozone is more typically from about 30 minutes to about 2 hours.

The gelling that can occur during the hydroprocessing is essentially due to the cross-linking of the elastic polymer in the emulsion. Treating the emulsion of the crosslinked elastic polymer with ozone causes an ozonolysis reaction. In this ozonolysis reaction, double bonds remaining in the crosslinked rubber are attacked, and ozonides are generated. Ozonides formed under low temperature reaction conditions are extremely unstable and are destroyed by hydrolysis with water in the latex. The crosslinked elastomeric polymer then cleaves, generally into low molecular weight rubber segments terminated with aldehyde groups. As ozonolysis continues, the initial aldehyde groups will subsequently be oxidized to carboxyl groups. The terminal aldehyde groups on the rubber segments can also be reduced to alcohols by adding a material such as sodium borohydride in ethanol, optionally at a temperature from about -20 ° C to about 0 ° C.
In each case, the resulting polymers are essentially non-crosslinked and soluble in common solvents for rubber. A solution of such a "soluble" polymer will pass through a 325 mesh screen.

After treating the latex with ozone, it can be used in a conventional manner. The latex can be coagulated to recover the dried rubber. Standard coagulation methods, such as salt-acid coagulation methods, can be employed. However, it should be noted that ozone treatment improves the stability of the latex, as soap-like polymer fragments with additional carboxylate end groups are formed. While this feature is often desirable, it requires the use of additional coagulants, the amount of which will be governed by the amount of carboxylate formed.

The present invention is described in more detail by the following examples. These examples are illustrative only, and should not be taken as limiting the scope of the invention or the manner in which it is implemented. Unless otherwise indicated, all parts and percentages are given by weight.

Example 1 Nitrile rubber latex was prepared by the method of Weideman 9
Hydrogenated to a saturation level of 6.2%. The latex was treated with oxygen and a small amount of hydroquinone, which reduced the residual hydrazine level to 58.5 ppm. About 150 ml of this latex was then charged to a beaker with a magnetic stirrer and treated with excess ozone (as an ozone / air mixture).
Samples were taken at 15 minute intervals and sealed in 20 ml vials. Another 150 ml sample was similarly treated with nitrogen as a control. Samples of the latex treated with nitrogen were also taken at 15 minute intervals. The collected samples were analyzed for residual hydrazine. Table 1 shows the results of these experiments.

As can be seen from Table 1, the level of residual hydrazine in the latex can be reduced to 3 ppm or less by ozone treatment. Therefore, the method of the present invention is an effective means for lowering the level of residual hydrazine in the latex to a very low level. Control experiments performed with the same flow rate of nitrogen as the air / ozone mixture also reduced the level of residual hydrazine in the latex. However, after treatment with nitrogen for 60 minutes, the level of residual hydrazine only dropped to 31.7 ppm. Producing a semi-log plot of the data shows that the rate of decrease in residual hydrazine levels is essentially first order for both ozone and nitrogen.

Example 2 A nitrile rubber latex was hydrogenated by the method of Weideman as described in Example 1. Latex sample
3 ml were coagulated in a methanol / saturated sodium chloride solution. Then 0.3 g of the polymer wetted with methanol and blotted was dissolved in a solution containing 15 ml of trichloromethane and 1 ml of acetonitrile. A very inert swollen gel was obtained. Although the molecular weight of the insoluble gel is inherently very high, small amounts of the polymer will dissolve in a suitable solvent, such as a mixture of trichloromethane and acetonitrile. The untreated partially soluble fraction has a number average molecular weight of 13
It was determined to have a molecular weight of 5,000, a molecular weight by weight of 543,000 and an intrinsic viscosity of 3.249.

A 150 ml sample of the hydrogenated latex was placed in a 400 ml beaker with a magnetic stir bar and treated with excess air / ozone at room temperature for at least 6 hours. After about 2.5 hours of ozone treatment, a portion of the latex was coagulated in a trichloromethane / acetonitrile solvent, but showed no gel.
Therefore, the ozone treatment of the present invention is an effective means for removing the gel formed by the Weidemann hydrogenation method. The recovered polymer is treated with ozone for about 2.5 hours, then the number average molecular weight is 16,000, the weight ratio molecular weight is 37,000, and the intrinsic viscosity is 0.22.
It was measured to have 5.

These examples show that the method of the invention can be used to remove gels and residual hydrazine from latex. Utilizing the present invention, the color of the latex is also improved by the removal of colored bodies, such as benzoquinone. Since the rubbers prepared by the process of the present invention contain terminal carboxyl groups, they can be cured with substances customary for curing carboxylated rubbers, such as zinc oxide or magnesium oxide. Since this rubber has an extremely high degree of saturation, a peroxide-based crosslinking agent,
For example, dicumyl peroxide, 2,5-bis (t-butylperoxy) -2,5-dimethylhexane or 2,5-dimethyl-2,5-di (t-butylperoxy) hexane-
It is also desirable to use 3.

While specific exemplary forms and details have been set forth to describe the invention, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the scope of the invention.

Claims (3)

(57) [Claims] 1. A method of treating a crosslinked elastomeric polymer emulsion containing residual hydrazine to obtain a latex of a soluble elastomeric polymer having a reduced residual hydrazine concentration by reducing the emulsion to at least half the level of residual hydrazine therein. Treating with a sufficient amount of ozone to reduce to a level of 0 to 60 ° C. for a period of 15 minutes to 6 hours to form a latex of a soluble elastomeric polymer having a reduced residual hydrazine level. Method. 2. The method according to claim 1, wherein the elastic polymer is a nitrile rubber having a degree of saturation of 94-99%. 3. The method according to claim 1, which is performed at a temperature in the range of 15-30 ° C.